Rheology and microstructure of sago starch from Papua New Guinea Original Research Article

The flow properties and microstructure of six sago starch samples from different localities (Kavieng, Kerema, Lae, Lorengau, Madang, and Wewak) in Papua New Guinea have been investigated. The rheological behaviour of 4% (w/w) paste was studied at 30°C, 40°C, 50°C, 60°C and 70°C, results were presented as shear stress–shear rate data and analysed using six yield stress and the power-law models. The viscosity was generally time-independent (CV=2–6%) and irrespective of the temperature, shear stress increased with the rate of shear for all the samples (pseudoplastic). The power-law model provided a good estimation (r=0.8739–0.9979) of the rheological behaviour with its index being 0.38±0.072 to essentially show no dependence on temperature and the source of the starch. The consistency index was temperature-dependent and Ea=9.8–23.0 kJ mol−1. Scanning electron microscopy revealed some damaged starch granules but granule morphology was identical for all the samples. The pH of the samples ranged from 3.7–5.1 and samples with low pH were generally of a low consistency index irrespective of the temperature.